<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <input type="text">
</body>
</html>
<script>
      //foucs、blur、change、input
      let ele = document.querySelector('input');

      //oninput,当表单元素的文本内容发生变化立马执行一次！！！
      ele.oninput = function(){
          console.log('123');
      }

</script>